The disclosure of Japanese Patent Application No. 2001-364447 filed on Nov. 29, 2001 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention generally relates to a control apparatus for a vehicular automatic transmission. More particularly, the invention relates to controlling the engaging force of a frictional engaging device when a gear is shifted from a driving gear to a non-driving gear.
2. Description of Related Art
A vehicular automatic transmission device having the following two elements has been known: (a) an automatic transmission attaining a plurality of gears having different power transmission states by selectively engaging and disengaging a plurality of frictional engaging devices, and having a driving gear for allowing power transmission and a non-driving gear for disconnecting power transmission; and (b) engaging-force control means for controlling engaging force of the frictional engaging devices when selectively engaging and disengaging the frictional engagement devices. One example of such an automatic transmission device is described in Japanese Patent Laid-Open Publication No. 1-229147. This automatic transmission device includes as the engaging-force control means a linear solenoid valve for controlling a hydraulic pressure of a hydraulic frictional engaging device. In this automatic transmission device, when a gear is shifted from a driving gear to a non-driving gear by disengaging the hydraulic frictional engaging device (clutch) (i.e., gearshift from xe2x80x9cdrive (D)xe2x80x9d to xe2x80x9cneutral (N)xe2x80x9d), the hydraulic pressure of the hydraulic frictional engaging device is controlled using a value such as that of a throttle valve opening as a parameter. In other words, the engaging force is controlled so as to disengage the clutch. A gearshift between a driving gear to a non-drive gear is commonly performed while the vehicle is stopped. In this state, however, power is transmitted from a driving power source (such as an engine) to the automatic transmission through a hydraulic transmission (such as a torque converter). In the driving gear in the state where the vehicle is stopped, the input revolution speed of the automatic transmission is zero, but driving torque is output to the wheel side. Therefore, if power transmission is disconnected as a result of gearshift from the driving gear to the non-driving gear, the driving torque is abruptly released, whereby shift shock may possibly occur.
Therefore, even if the engaging force is controlled as described in Japanese Patent Laid-Open Publication No. 1-229147, the engaging force is not necessarily controlled in a desired manner due to the individual differences of the frictional engaging devices and their control system, aging thereof, and the like. As a result, shift shock may possibly occur. Learning correction is effective for the individual differences and aging. For example, it is possible to conduct learning correction of the engaging force based on a change in input rotational speed to the automatic transmission caused by a gearshift from a driving gear to a non-driving gear, that is, based on an increase in input rotational speed to a value close to the rotational speed of the driving power source caused by disconnection of power transmission. However, the time required for a gearshift from the driving gear to the non-driving gear is generally very short, such as one second or less, and normally about 0.5 seconds or less. Moreover, the input rotational speed is zero before the gearshift. It is therefore difficult to detect a change in input rotational speed with high accuracy. As a result, learning correction cannot be performed in a sufficiently satisfactory manner. It is generally difficult for a currently used rotational speed sensor to detect a rotational speed of about several hundreds of rpm or less with high accuracy.
It is an object of the invention to minimize shift shock generated by a gearshift when making a transition from a driving gear to a non-driving gear, i.e., a gearshift whose learning correction is difficult, in an excellent manner regardless of the individual differences of frictional engaging devices, their control system, aging thereof, and the like.
A first aspect of the invention relates to a control apparatus for a vehicular automatic transmission that attains a plurality of gears having different power transmission states by selectively engaging and disengaging at least one of a plurality of frictional engaging devices including first and second frictional engaging devices, and includes an engaging-force control device that controls, when selectively engaging and disengaging the frictional engaging devices, engaging force of the selectively engaged and disengaged frictional engaging devices. This control apparatus includes a controller that performs learning correction of the engaging force of the first frictional engaging device based on a predetermined control parameter when performing a prescribed first gearshift between the gears, and corrects the engaging force of the second frictional engaging device based on the learning correction performed by the controller when performing a second gearshift different from the first gearshift. In the first gearshift, the first frictional engaging device is selectively engaged and disengaged and the engaging force of the first frictional engaging device is controlled by the engaging-force control device. In the second gearshift, the second frictional engaging device is selectively engaged and disengaged and the engaging force of the second frictional engaging device is controlled by the engaging-force control device.
In the first aspect of the invention, the engaging force of the second frictional engaging device, which is controlled by the engaging-force control device in the second gearshift, is corrected using the learning correction which was performed based on the predetermined control parameter by the controller in the first gearshift different from the second gearshift. By using the learning correction of the first gearshift in order to control the engaging force in the second gearshift, learning correction of the second gearshift can be eliminated, whereby the overall control of the engaging force can be simplified.
A second aspect of the invention relates to a control method for a vehicular automatic transmission that attains a plurality of gears having different power transmission states by selectively engaging and disengaging at least one of a plurality of frictional engaging devices including first and second frictional engaging devices, and includes an engaging-force control device that controls, when selectively engaging and disengaging the frictional engaging devices, engaging force of the selectively engaged and disengaged frictional engaging devices. The control method of the second aspect includes the steps of performing learning correction of the engaging force of the first frictional engaging device based on a predetermined control parameter when performing a prescribed first gearshift between the gears. In the first gearshift, the first frictional engaging device is selectively engaged and disengaged and the engaging force of the first frictional engaging device is controlled by the engaging-force control device. The controller corrects the engaging force of the second frictional engaging device based on the learning correction performed in the first gearshift when performing a second gearshift different from the first gearshift. In the second gearshift, the second frictional engaging device being selectively engaged and disengaged and the engaging force of the second frictional engaging device is controlled by the engaging-force control device.
In the invention, the second frictional engaging device may be substantially identical to the first frictional engaging device, i.e., the second frictional engaging device may serve as the first frictional engaging device.